There are many options for lighting:
T12 and T8 florescent bulbs (these are what come in most stock lights... lower wattage and less light than other alternatives, but can still work if there is enough wattage over the tank)
T5HO (t5 high output florescent lights): These are popular in both reef tanks and planted thanks. They are higher wattage than T8 or T12 bulbs of the same length. The fixtures tend to be expensive, but are some of the best lights for growing plants
Compact Florescent Lights: Come in many forms, ranging from cheap to expensive. They work well for plants, and generally put out more wattage than standard T8 and t12 bulbs.
LED Lighting: Just emerging onto the planted tank scene. Never used them, but lots of people get good results with them. Can be economical if you build your own fixture. Off the shelf fixtures tend to be pretty pricey
Metal Halide: Very powerful lighting, used on pretty much just the largest planted tanks. They are much more popular for use on reef tanks. They put off a lot of heat, and are very expensive.
If you tell us what kind of lighting you currently have (type of bulb, color temp of the bulb, wattage, etc) we can let you know what your expected results for growing low light plants with it will be.
As far as CO2 injection: Plants need CO2 during photosynthesis. There is some CO2 in water (water will equalize with the concentration of CO2 in the air). We have found that in the planted tank hobby, injecting additional co2 into the water column does wonders for plant health, growth, and controlling algae. There are a few different methods to it (pressurized systems versus DIY systems). It is not a requirement to inject CO2 to have a planted tank (at least not until you move into the realm of high light). However, there are some plants in the hobby that are hard to keep alive in a tank without injecting CO2 into the water and without putting very powerful lights over the tank.